As result of the increasing number of on-site repairs to transformers, bottlenecks in coil manufacture in individual manufacturing locations of a transformer plant, and the simultaneously free winding capacity at other locations, the transportation of coils for oil-filled transformers less than 1000 kVA and pre-assembled coil blocks without the associated transformer tank and without associated cores is acquiring greater importance.
Coils for oil-filled transformers are generally transported (A) completely dry, (B) vertically and axially clamped with a defined force, (C) radially supported, and (D) complying with specified width and height dimensions.
The specification according to (A) results from on-site repairs, where technical equipment for drying the coils is not usually available and the technical equipment cannot be provided at a reasonable expense. When coils are transferred between different manufacturing locations without dry transportation, the coils are first dried before installation, which often results in time and capacity problems.
The specification according to (B) results from the fact that coils have to be fitted in a short-circuit-proof manner, axially clamped under a defined force and thereby set up under pressure to a defined installation length. However, the technical prerequisites for pressing coils and coil blocks are not usually available on site. For example, when coils are transferred between different manufacturing locations, the same time and capacity problems can occur as with drying. In addition it is not technically possible to transport coils without any axial clamping.
The specification for radial support when transporting coils according to (C) results from the fact that coils and coil blocks mounted on the active part are supported by the solid core legs. Their construction with correspondingly thin supporting cylinders is not designed for unsupported transportation. Thus, it is not possible to transport coils without radial fixing or support.
The specification according to (D) result from width dimensions which, in the case of land transport, arise from the width of the roadways to be used and the building regulations for trucks derived therefrom, and from height dimensions which are derived from necessary bridge clearances and similar. The same also applies to rail transport. In the case of sea transport, in addition to the above-mentioned specifications, container dimensions and the specifications relating to stackability are also taken into account.
According to known transport housings, when transporting coils or coil blocks, the specifications according to (B) and (C) are usually implemented by fitting the coils or coil blocks into a press frame consisting of lower and upper pressing plate and tie rods for fixing under pressure.
According to known transport housings, the specifications according to (A) is usually fulfilled by transporting the coils in pressure-tight transport tanks, which are specially designed for this means of transport and are therefore expensive. Thus, the use of a transport tank can be restricted to one or sometimes a few means of transport. For example, the press frame with the coils is placed and fixed in this transport tank and then screwed pressure-tight by means of a cover. In order to provide protection against moisture during transportation, this configuration is then either filled with dry air, and a positive pressure is maintained in the tank by means of an attached system with a pressure cylinder for the entirety of the transportation period. Alternatively, the transport tank can be filled with dried transformer oil and an oil-free space between the top of the coil and the bottom of the tank is connected to the external atmosphere via an air dryer, which is used to balance the temperature. At the same time, the external dimensions of the transport are a consideration.
The previous implementation of the processes according to (A) for dry transportation by means of transport tanks due to their construction and their manufacture, uses pressure-tight transport tanks, which are very expensive, i.e. the price of a transport tank is up to 40% of the cost of the leg coils to be transported.
When transporting with dry air, the maintenance of the positive pressure is monitored at regular intervals during transportation.
The additional dimensions for transport tank, cover, compressed air system or dry air storage for oil transportation with air cushions reduce the space remaining for the coil block itself in the given transport volume.
Above a certain coil size, cost-intensive special transport means, including night travel, single lane closures, police escort etc., may be used depending on the dimensions of the pressed coil block.
In the case of on-site repairs, the associated additional costs have been be taken into account and up to now, the high transport costs have prevented coils being transferred between different manufacturing locations to make use of free winding capacity for want of appropriate cost effectiveness.